1. Field of the Invention
The present invention is directed to a method of manufacturing thin film iris diaphragms for use in corpuscular beam apparatus such as electron microscopes and vidicons which iris diaphragms consist of a metal layer containing at least one opening in order to pass a beam of particles.
2. Prior Art
Iris diaphragms have been previously made from two separately manufactured components comprising a metal layer and a substrate or carrier plate. The metal layer is produced by depositing the metal on a profile surface of a template using a vapor metal deposition technique conducted under vacuum conditions. After forming the layer on the template, it is removed and secured to the substrate or carrier plate such as by brazing.
Since the rate of fouling of an iris diaphragm increases with the thickness of the metal layer, the metal layer must be as thin as possible. Due to this requirement for a thin layer, the above described process has a high risk of damage to the metal layer as it is being removed from the template and during the step of securing it to the carrier or substrate. In addition thereto, the above described process requires templates which are complex and expensive to manufacture and which can only be used a few times.
To overcome the above mentioned problems in the manufacture of iris diaphragms, it has been suggested to produce the diaphragms with the following method. A metal film is deposited directly on a carrier using for example electro-deposition methods with an appropriate mask. The carrier is subsequently etched in the area adjacent to the opening of the thin metal layer by a positive etching technique. Since the etching agent can only attack the unprotected areas of the carrier plate, the metal film or layer and the carrier must be made of different metals. While this process overcomes several difficulties experienced with the previous method, the different in the coefficience of thermal expansion and the difference in the thermal conductivity of the two metals used for the carrier member and the thin film subjects the iris diaphragm to distorsion when used in an apparatus subjected to temperature fluctuations. Thus, the thin film iris diaphragms produced by the proposed method are unsuitable for corpuscular beam apparatuses of the kind in which major temperature fluctuations will occur.